Source : WordNet®

undistinguishable
     adj : not capable of being distinguished or differentiated; "the
           two specimens are actually different from each other
           but the differences are almost indistinguishable"; "the
           twins were indistinguishable"; "a colorless person
           quite indistinguishable from the colorless mass of
           humanity" [syn: {indistinguishable}] [ant: {distinguishable}]